Unhexennium
Unhexennium, Uhe, is the temporary name of element 169. Nuclear Properties At least one set of theoretical values for half-lives and decay modes of Uhe have been constructed for neutron count up to N = 333(3). It predicts isotopes ranging from Uhe 458 to Uhe 501 in two bands: Uhe 458 to Uhe 483 and Uhe 498 to Uhe 501. Examination of pp 15 & 18 of Ref. 3 indicates that Uhe 458 through Uhe 483 are part of the expected pattern of alpha-decaying nuclei centered on the N = 308 shell closure: Uhe 458 to Uhe 461 decay by fission and have sub-microsecond half-lives, while Uhe 462 to Uhe 483 decay by alpha emission with half-lives ranging up to about 1 ms, and possibly 1 sec in the case of Uhe 477. Uhe 498 to Uhe 501 might indicate a shell closure near N = 330, but they are also located in a region whose patterns of half-lives and decay modes indicates that the model may have reached the limits of its capability. What Ref. 3 can’t do is describe heavy isotopes of Uhe. It is possible to use a first-order, liquid-drop approach to guess at what lies there. At least two computations of the neutron dripline’s location up to Z = 175 exist(4),(5), and since they give similar results, the maximum possible size of a Uhe nucleus can be set slightly above the values computed, allowing only a small margin for error. This gives Uhe 605 as the heaviest possible Uhe isotope. Similarly, a realistic lower bound can be set by requiring that the amount of energy needed to stabilize a nucleus be no more than twice what is needed to stabilize Usp 471. Within this range, the liquid-drop model can be used to indicate the amount of structural correction energy needed to allow a drop of nuclear matter to survive for the 10^-14 sec needed for electromagnetic interactions (such as binding an electron) to become important. Structural correction required for Uhe 605 itself is around 1 MeV, which means all Uhe drops will fission quickly without structural stabilization. In general, it is not possible to describe structural correction energy. What can be predicted are neutron and proton shell closures, for which correction energy is expected to be particularly large. Neutron shell closures have been predicted at N = 406(5),(6), 370(5), 318(7), and 308(1). The isotope Uhe 575 requires around 1.5 MeV of structural correction, which means isotopes in the Uhe 565 to Uhe 580 band are likely. (See “Formation” for additional significance of these nuclei.) Uhe 539 requires 1.5 MeV of structural correction, which means isotopes in the band Uhe 529 to Uhe 544 are also likely. All isotopes in both bands should beta-decay with half-lives under a second. On the other hand, Uhe 487 requires 3.5 MeV of correction energy, which means it is likely to stabilize some nuclei in its vicinity. Ref. 3 does not show a pattern of nuclides which indicate a shell closure at N = 318. Uhe 477 requires 4.5 MeV of correction energy, which is realistic for a strong neutron shell closure, such as the one predicted at N = 308, so the liquid-drop picture isn’t unrealistic. Atomic properties Several predictions for the ground state electron structure of Uhe agree that it will have p-block character, with two 9s, two 9p1/2, and one 8p3/2 electrons available for bonding. Electrons in Uhe can be described in terms of time-independent orbitals, but calculation of electron properties require that nuclear charge be distributed over the nucleus' actual volume. In addition, there is some chance that differing nuclear shapes may produce different electron configurations in different isotopes. (Different isotopes would be different elements in the chemical sense.) Except in the laboratory, Uhe is expected to exist only in environments too hot for ordinary chemistry to occur. Formation FORMATION Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. There is a possibility that beta decay from dripline nuclides stabilized by the N = 406 closure, enhanced by the Z = 164 proton shell closure, will allow some isotopes in the vicinity of Uhe 565 to Uhe 577 to form in quantity during such a merger. It improbable that nuclides between Uhe 529 and Uhe 544, or lighter, can form in this way. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Uhe 458 to Uhe 483 band. Quantities produced by this method are very small. REFERENCES 3. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 4. "Neutron and Proton Drip Lines Using the Modified Bethe-Weizsacker Mass Formula; D.N. Basu et al; Int.J.Mod.Phys.; arXiv:nucl-th/0306061; url: https://arxiv.org/abs/nucl-th/0306061 5. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 6. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 7. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (12-12-19) References Category:Undiscovered elements Category:Alkali metals Category:Radioactive